• Question: Why cant we feel the earh spinning?

    Asked by tiioshax to Daniel, Jon, Louise, Sharon, Zoe on 21 Jun 2010 in Categories: . This question was also asked by kavi963, nidhi6.
    • Photo: Sharon Sneddon

      Sharon Sneddon answered on 18 Jun 2010:

      Earth moves very fast. It spins at a speed of about 1,000 miles per hour at the equator and orbits around the sun at a speed of about 67,000 miles per hour. We do not feel any of this motion because these speeds are constant. The spinning and orbital speeds of Earth stay the same so we do not feel any acceleration or deceleration. You can only feel motion if your speed changes. For example, if you are in a car which is moving at a constant speed on a smooth surface, you will not feel much motion. However, when the car accelerates or when the brakes are applied, you do feel motion. Hope this makes sense!

    • Photo: Jon Copley

      Jon Copley answered on 18 Jun 2010:

      How are you sure that we can’t? Maybe the “normal” way we feel is because always feel the Earth spinning. And perhaps the “space sickness” that astronauts get for the first few days when they leave the Earth is because they have to adjust to not feeling it any more?

    • Photo: Louise Dash

      Louise Dash answered on 20 Jun 2010:

      The earth is spinning on its axis at a rate of one revolution per day, so if you’re at the equator you’re travelling at about 1000 miles an hour! There’s also the earth orbiting around the sun at around 67,000 miles an hour. So we should be able to feel that, right?

      The reason we don’t is because we’re travelling at a constant speed* – and we can only feel *changes* in velocity when we speed up or slow down. For instance, you can feel it when you’re in an accelerating car because you’re pushed back against your seat, but if you’re in an aeroplane going at a constant 500 miles an hour, you can’t really tell you’re moving at all.

      But our speed isn’t completely constant, because we’re not moving in a straight line, we’re rotating, which actually means we are accelerating (I won’t go into the maths of this, but let me know if you want me to!) and are therefore subject to a force. This is the same force that you feel when going round a sharp corner in a car, or on a merry-go-round, that makes us feel as though we’re being pushed away from the centre of the curve.

      The reason we don’t feel this force pushing us away from the earth is because it’s very weak. The strength of this rotational force depends on how long it takes to make a rotation, not on how fast we’re actually moving. It takes a whole day for the earth to make one rotation, which is actually quite slow! If the earth rotated faster, we’d feel this force more strongly. And as this force is strongest at the equator (because the radius of the rotation is greatest there) and weakest at the poles, this means if you go and stand near the equator you will weigh (a tiny bit) less!

    • Photo: Zoe Duck

      Zoe Duck answered on 21 Jun 2010:

      Because it spins at a constant speed. We feel things moving due to the acceleration produced (changes in speed). As the earth spins at a constant rate we dont notice it spinning

Comments

  • Photo: tiioshax

    tiioshax commented on :

    Thank You Sharon…It Makes Alot Of Sense 🙂 ….And Thank You Too John x

    • Photo: Jon

      Jon commented on :

      I agree with Sharon’s answer, but I have one nagging thought in my mind… An object will stay in constant motion if it doesn’t have a force acting on it. So it is certainly true that we wouldn’t feel constant motion, because there is no force involved.

      But constant motion, without any forces, is always straight-line motion. For an object to move around in a circle, a force has to be acting on it. So why can’t we “feel” that force as the Earth spins? If I’m on a roundabout in a playground, even it is spinning at a constant speed, I can still feel that I am on a spinning roundabout if I shut my eyes…

      So I think there’s a bit more to answering the question… and I’ll try to get back to you when I’ve had a think about it a bit more!

      • Photo: Sharon

        Sharon commented on :

        In an attempt to further increase my knowledge on this question Jon, I went on a roundabout today and shut my eyes. I’m pretty sure it was spinning fairly constantly, and yes, I could feel that I was moving!!!! My nephew thought I was slightly crazy, but I told him it was an important scientific experiment!!!

        I look forward to your explanation!!

        • Photo: Jon

          Jon commented on :

          Wow – that’s great Sharon, many thanks for doing the experiment! I’ve had a think, and maybe have come up with a bit more explanation for why we don’t feel the Earth spinning – unlike your roundabout.

          When you are on a roundabout, the force that you feel is “centrifugal force”, which feels like it is pulling you towards the edge of the roundabout. We have centrifugal force on the spinning Earth too – and it always pulls in the direction 90 degrees away from the axis of the Earth’s rotation (that axis is the line through the Earth between the North and South Poles).

          So why doesn’t that centrifugal force make us fly off the Earth and into space? (Imagine if you are on a roundabout, and you let go of a ball: it will carry on in a straight line from where you let go, flying off the roundabout as you continue to turn on it).

          Fortunately for us, gravity cancels the effect of the centrifugal force and keeps us rooted to the spot. So I think that’s why we don’t feel the Earth spinning – although there are forces involved (and so it’s not quite the same as straight-line constant motion), we don’t feel them because the Earth’s gravity cancels them out. And we do feel the Earth’s gravity, whenever we walk around or lift things!